The pathogenesis of cystic fibrosis (CF) lung disease remains unclear. One hypothesis is that defects in the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) in the respiratory surface epithelium leads to abnormal ion transport, which alters the physical characteristics and volume of airway lining fluid; this, in turn, results in decreased mucociliary clearance and chronic bacterial infection. An alternative hypothesis is that the absence of CFTR in the submucosal gland epithelium causes abnormal mucus production that leads to bacterial colonization and chronic airway inflammation. The objective of this proposal is to determine the relative importance of surface and submucosal gland epithelium in the pathogenesis of CF. A well-established human airway xenograft model in which human airway segments are heterotopically transplanted into Severe Combined Immune Deficient (SCID) mice will be used to relate transepithelial ion transport to mucus properties, mucociliary clearance and bacterial adhesion in xenografts from CF and non-CF airways. Baseline transepithelial potential difference (PD) and responses to amiloride, cAMP agonists and low chloride solution will be determined iii vivo and in modified Ussing chambers. Sulfation of high molecular weight glycoconjugates from xenografts, mucus rheology, mucociliary clearance and pseudomonal adhesion will be determined. After baseline characterization, CFTR gene transfer to surface airway epithelium will be performed using an adenoviral vector. Transgene expression will be localized and quantified by in situ hybridization and immunocytochemistry. To detect the relative importance of CFTR function in surface and submucosal gland epithelia, the efficiency and distribution of CFTR expression after gene transfer will be correlated with changes in ion transport, mucus properties. mucociliary clearance, and bacterial adhesion. This will provide insight into the pathophysiology of airway disease in CF, and thereby assist in the design of rational gene therapy and pharmacologic approaches.